What is known about the Telegony?

Factual Questions
1

The Odyssey movie prompted me to reread Stephen Fry’s version of the story. After the ending, Fry says:

But Odysseus’s debt to Poseidon is not yet fully discharged. The price he has to pay for poking that stick in Polyphemus’s eye is high indeed. If you recall, when he visited Hades, Tiresias told him: Finally home and in the bosom of your wife and son, scores settled and peace established at your hearth, you will immediately have to leave Ithaca, an oar on your shoulder, to search for the land whose people have never heard of the sea, who use no salt, have no understanding of ships or sailing, and do not so much as know what an oar is. When a stranger hails you there, points at the oar on your shoulder, and asks why you are carrying a winnowing fan, you are to plant the oar in the ground, make sacrifices to Poseidon and, as you make your way back home, to each of the twelve great gods in turn. Homer is of no use to us now. Instead, the major source for post-Homeric Odyssean doings is the Telegony, a lost manuscript of disputed authorship that tells the adventures of Telegonus, Odysseus’s son by Circe. 124 “Telemachus” means “warrior far away,” and “Telegonus” means “born far away.”125 Odysseus was nothing if not a remote father.

Is anything known about this lost work?

2

As shouldn’t be suprising, there is a significant Wikipedia article.

3

I’ve heard of it.

4

So no happy ending for Odysseus? And can’t Poseidon just let it go? His one-eyed son was happily munching on Greek warriors when Odysseus finally put a damper on it by blinding him. Does Polyphemus not bear any responsibility, for gods’ sake?

5

No doubt Wikipedia is useful. But it is not necessarily academic, and perhaps some people here know other things. I’d never really heard of these stories, but the amount of ancient knowledge lost to neglect must be considerable.